(1) Field of the Invention
The present invention relates to a color image forming apparatus, such as a digital color copying machine.
(2) Description of the Prior Art
In a conventional digital color copying machine, color correction is performed so as to obtain image copies without causing deterioration. However, there has been a problem that, since a color correction value used in the color correction is a fixed value, the color reproducibility deteriorates when the color characteristics of an ink film or the recording density characteristics of a recording paper changes with time. Japanese Laid-open Patent Application No. 2-199964 discloses a color correction technique which is able to cope with the varying color characteristics of an ink film or the varying recording density characteristics of a recording paper. According to the technique disclosed in that application, a sample patch formed in accordance with conventional color data is printed on a recording paper, and a color correction value is changed depending on the color data read from the sample patch and the conventional color data.
In the prior art, as the color correction value can be changed depending on the reproduction characteristics of the image forming apparatus, the color reproducibility in a copy is stabilized. However, when making second, third, and successive generation copies of an original, there is a gradual deterioration in image quality and color, so that the colors in a later generation copy end up being totally different from the original colors. Here, even if the image forming apparatus reproduces the colors and the image quality as close to the original as possible, the colors in the copied image will still be different from the original colors due to the influence of the toner graininess and the characteristics of each color. If a copied image is copied further, the colors and the image quality become even more different from the original colors and the original image quality. The difference between the original image and the copied image becomes greater as the process of making copies of a copied image is repeated.
Repeating making copies of a copied image results not only in poor color reproducibility but also in deterioration of the minute line reproducibility and the gradient characteristic reproducibility.
The principal object of the present invention is to provide an image forming apparatus which is capable of forming an image with guaranteed reproducibility of colors, fine lines and gradations, even when it repeats reproduction to make generations of copies.
The principal object of the present invention is to provide an image forming apparatus which is capable of forming an image with guaranteed reproducibility of colors, fine lines and gradations, even when it repeats reproduction to make generations of copies.
The above object can be achieved by producing a color image forming apparatus comprising: a standard pattern data storage unit for storing standard pattern data for color correction; a standard pattern forming unit for forming a standard pattern for color correction on a copying paper in accordance with the standard pattern data; a standard pattern reading unit for reading the standard pattern formed on a document to be read; a color correction condition modification unit for modifying color correction conditions in accordance with standard pattern data obtained by reading the standard pattern formed on the document and the standard pattern data stored in the standard pattern data storage unit in advance; and a correction unit for performing color correction on read data of the entire image of the document in accordance with the modified color correction conditions.
The object of the present invention may also be achieved by providing an image forming apparatus comprising: a standard pattern data storage unit for storing standard pattern data for gradation correction; a standard pattern forming unit for forming a standard pattern for gradation correction on a copying paper in accordance with the standard pattern data; a standard pattern reading unit for reading a standard pattern formed on a document being read; a gradation correction condition modification unit for modifying gradation correction conditions in accordance with the read standard pattern data and the stored standard pattern data; and a correction unit for correcting image data obtained by reading the document in accordance with the modified gradation correction conditions.
The object of the present invention may also be achieved by providing an image forming apparatus comprising: a machine code storage unit for storing machine codes in advance; a standard pattern reading unit for reading a standard pattern formed on a document, the standard pattern corresponding to one of the machine codes; a machine code fetch unit for fetching a machine code corresponding to standard pattern data obtained by reading the standard pattern; a gradation correction condition modification unit for modifying gradation correction conditions in accordance with the fetched machine code; and a correction unit for correcting image data obtained by reading the image of the document in accordance with the modified gradation correction conditions.
The object of the present invention may also be achieved by an image forming method used for an image forming apparatus which comprises: a document reading unit for optically reading a document; a correction unit for performing color correction and gradation correction on image data obtained by reading the document; a storage unit for storing standard pattern data to be standards for correction; and an image printing unit for printing an image on a copying paper in accordance with the corrected image data. The image forming method comprises the steps of: reading the standard pattern data stored in the storage unit and forming a standard pattern in a predetermined area on the copying paper; reading the document by the document reading unit; detecting the standard pattern data from the image data; comparing the detected standard pattern data with the standard pattern data stored in the storage unit, determining color correction conditions, gradation correction conditions, and MTF correction conditions, and setting them in the correction unit; and correcting the image data in accordance with the corrected correction conditions and forming an image on the copying paper.
The object of the present invention may also achieved by an image forming method used for an image forming apparatus which comprises: a document reading unit for optically reading a document; a correction unit for performing gradation correction on image data obtained by reading a document; and an image printing unit for printing an image on a copying paper using a table containing machine codes and corresponding gradation correction conditions, and the corrected image data. The image forming method comprises the steps of: reading a document; detecting a standard pattern from the image data; detecting a machine code represented by the detected standard pattern; reading gradation correction conditions corresponding to the machine code detected from the table, and setting them in the correction unit; and correcting the image data by the correction unit, and printing the image on the copying paper.